I suggest you ...

Master page inheritance

Hi. I think It would be great if there is some kind of master page inheritance. For instance: I have two masters pages (A) that has some elements. Then I create another master page (B) that inherits from A and has other elements. And then a page (X) that inherits from A and another page (Z) that inherits from B. If I change any element on A it will affect master B, X, and Z. But if I change B it will only affect X.

I agree. I think the same result can be obtained if you can have multiple masters on a page, not only one. Inheritance would be a plus, but alone it does not solve the problem I think.

Example for me : main navigation is a Master, and main content layout is a Master, but I cannot use both in the same page. It's annoying, cause I'm obliged to merge one with the page to see toe full picture.

There is a suggestion by another user to see masters as objects instead of pages, but I think it is also the same idea.